The present invention relates to a radiation-polymerizable composition. More particularly, this invention relates to a radiation-polymerizable composition which may be employed to produce an improved photographic element such as a lithographic printing plate. Such plates show an increase of stability and press run life. The composition can be readily formed into adherent coatings useful in the graphic arts especially in the production of lithographic printing plates.
The use of radiation polymerizable coatings in the graphic arts is well known. Typically, the composition of such coatings can include a polymeric constituent, which may itself be radiation polymerizable, and a photosensitizer composition. Upon selection exposure of this coating to imaging energies, the radiation polymerizable species within the composition would either itself undergo a reaction or promote a reaction or degradation of one or more of the other components of the composition. It is, of course, readily appreciated that such reaction is only of value in such a system where it is essentially confined, or limited, to those areas of the composition impinged upon by such imaging energies. A negative working image thus created within the coating can then be "developed" by selective removal of the non-exposed components of the film or layer which have not been subjected to imaging energies. The ability to create such selective changes in coatings prepared from a radiation polymerizable composition has been appreciated for some time. The basic difference in the various approaches in the formulation of lithographic printing plates from radiation polymerizable compositions has been in the search for a system which is prepared from relatively inexpensive ingredients, does not require prolonged imaging energies (has a high quantum efficiency) is able to undergo an increased number of press runs, results in the creation of high resolution images within the composition which can be manifested without prolonged and elaborate development and, most significantly, may be developed with a composition which does not necessarily contain organic solvents and need only contain a minimal amount of salts and surfactants.
Most such lithographic printing plates comprise a metal substrate which is coated with a light sensitive diazonium compound in admixture with suitable binding resins, photoinitiators, photopolymerizable compositions, colorants, stabilizers, exposure indicators, surfactants and the like.
Although the art is replete with photosensitive compositions which may be used for lithographic printing plates, the prior art composition's serviceability is restricted by their limited stability and number of press runs.
It is desired to produce a composition for use in lithographic printing plates which is relatively oxygen insensitive, substantially eliminating the need to expose a screen prepared with a protective barrier layer or the addition of diazonium or cation forming compounds.